1. Field of the Invention
The present invention relates generally to an apparatus and method for measuring and redistributing transmission power when allocating a radio frequency band resource in a Space Division Multiple Access (SDMA) system.
The present invention provides a technique for efficiently allocating a radio resource when integrating and allocating several bands to a Mobile Station (MS) in a Space Division Multiple Access (SDMA) system for dividing the radio resource into a frequency band and allocating the divided radio resource.
2. Description of the Related Art
An Institute of Electrical and Electronic Engineers (IEEE) 802.16 Wireless Metropolitan Area Network (MAN) system is a typical example of an SDMA system for dividing a radio resource into a frequency band and allocating the divided radio resource.
FIG. 1 illustrates the downlink frame architecture used in the SDMA system.
Referring to FIG. 1, a DownLink (DL) frame of the SDMA system is divided into preamble and MAP information on an entire frame, a Non Adaptive Antenna System (AAS) traffic zone not supporting SDMA, and an AAS zone supporting the SDMA. The AAS zone is again divided into 12 bands based on a frequency axis. A data burst is provided on a per-band basis and transmitted to an MS. Each band has channel qualities different from each other for one MS.
The AAS zone has a minimum size of one band as a radio resource allocated to the MS. However, in case where the MS sends a request for allocating a data burst having a size of one or more bands to a Base Station (BS), the BS can merge several bands into one data burst and allocate the radio resources. Particularly, when receiving only one data burst per frame because, of limitation to its performance or a need to reduce the MAP information in size, the MS necessarily needs a method for merging several bands into one data burst and allocating a radio resource.
An inefficient example of merging a plurality of channel bands into the data burst and allocating the radio resource will be described with reference to FIG. 2 below.
FIG. 2 illustrates an example of allocating, by the BS, the data burst including the plurality of channel bands in the SDMA system.
Referring to FIG. 2, the BS merges AAS Bands #1, #2, and #3 into one data burst, and allocates a radio resource to the MS. Resource #1 and Resource #2 refer to radio resources allocated to the same position by the SDMA system. The Resource #1 is allocated to a User #1 MS, and the Resource #2 to a User #2 MS.
In FIG. 2, the BS fixedly distributes a transmission power (PWR) by 0.5 on a per-resource basis. When the BS distributes the transmission power by 0.5, the MS has a Carrier to Interference and Noise Ratio (CINR) and a Modulation order Product code Rate (MPR) corresponding to the CINR at each band as shown in FIG. 2. In this case, a fixed transmission power per band is 0.5 because the User #1 MS and the User #2 MS share the Resource #1 and the Resource #2, the radio resources of the same position. Here, the MPR, which is a rate of an amount of information transmitted using the radio resource of the same size, corresponds to the CINR.
In case where the transmission power is distributed by 0.5 as shown in FIG. 2, AAS Band #1 and AAS Band #3 of the Resource #1 have an MPR of 1.5 but AAS Band #2 has an MPR of 0.5. Therefore, the User #1 MS has available a final Target MPR of 0.5. Accordingly, the User #1 MS is inefficient because a low CINR of the AAS Band #2 of the Resource #1 results in reduction of a total Target MPR. Alternatively, AAS Band #2 of the Resource #2 has an MPR of 2.0 but AAS Band #1 and AAS Band #3 have an MPR of 1.0 when the transmission power is fixedly distributed by 0.5. Therefore, the User #2 MS has a Target MPR of 1.0 and thus, results in a waste of the transmission power in the AAS Band #2 of the Resource #2.